Evolution and dynamics of summertime blocking over the Far East and the associated surface Okhotsk high
Evolution and dynamics of summertime blocking over the Far East and the associated surface Okhotsk high
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DOI：
10.1256/qj.03.101
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发表时间：
2004-04
影响因子：
8.9
通讯作者：
H. Nakamura;T. Fukamachi
中科院分区：
文献类型：
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作者：
H. Nakamura;T. Fukamachi
通过对不同的地面高压事件进行合成分析，研究了远东上空上层阻塞脊和鄂霍次克海上空相关地面高压的时间演变和动力学，这些高压导致日本东部夏季异常凉爽。阻塞的形成机制和垂直结构在5月和7月之间有根本的不同，这归因于急流结构的季节性变化，远东地区的风暴轴活动以及鄂霍次克地区的海陆热力对比。在5月，来自迁移涡旋的强迫足够强，使得在北太平洋上缓慢后退的反气旋异常发展成阻塞脊。在鄂霍次克地区弱的海陆热力对比下，高压脊保持相当正压。相反，在西风带减弱和分裂的情况下，涡动强迫不再是7月份阻塞形成的主要因素。相反，从北方欧洲上空的对流反气旋异常发出的静止Rossby波包的传播在远东地区停滞，随后波包的局部破裂导致阻塞形成。在1993年7月的一个特殊情况下，在前两个星期，与阻塞形成有关的波包可以追溯到远至北美东海岸的上游。阻塞高压脊引起的异常地面东风，在7月较强的冷海面与西面暖陆块的热力对比作用下，通过冷平流建立冷地面反气旋，使阻塞异常具有明显的斜压性。版权所有© 2004年皇家气象学会
Time evolution and dynamics of an upper‐level blocking ridge over the Far East and the associated surface high over the Sea of Okhotsk that give rise to abnormal summertime coolness over eastern Japan are investigated through a composite analysis applied to distinct surface high events. The formation mechanism and vertical structure of the blocking differ fundamentally between May and July, attributable to seasonal changes in the jet structure, storm‐track activity over the Far East and the land–sea thermal contrast within the Okhotsk region. In May, forcing from migratory eddies is strong enough for precursory anticyclonic anomalies retrograding slowly over the North Pacific to develop into a blocking ridge. The ridge remains equivalent barotropic under the weak land–sea thermal contrast in the Okhotsk region. In contrast, the eddy forcing is no longer the primary factor for the blocking formation in July, in the presence of the weakened and split westerlies. Rather, the propagation of a stationary Rossby wave packet that has emanated from precursory anticyclonic anomalies over northern Europe stagnates over the Far East, and the subsequent local breaking of the packet leads to the blocking formation. In a particular case in July 1993, a wave packet involved in blocking formation could be traced back as far upstream as the east coast of North America over the two previous weeks. Acting on the strong thermal contrast in July between the cool sea surface and a warm land mass to the west, the anomalous surface easterlies induced by the blocking ridge can build up a cold surface anticyclone through cold advection, rendering the blocking anomalies distinctly baroclinic. Copyright © 2004 Royal Meteorological Society